high voltage

[rlcorley70]

have 04 dodge ram 3500, just replaced batteries and alternator, thought everything was good ,started just fine but noticed volt meter guage was running on the low side.
with engine off volts at battery just over 12 but when running drops down to around 11. so I tested voltage at alternator when running and its up at 38 volts. surprised I haven't melted the batteries. I can't figure out whats causing the high voltage any help would be greatly appreciated. oh yeah after I had my 38 volts took alternator to have bench test done and it showed 14.6 v, what the heck is my problem here?

 

[BamaRam]

Check voltage drop between batteries. On DC scale, put one lead on the positive battery post (not the terminal). Put the other lead on the opposite side positive battery post. Meter should read zero volt give or take .5vdc. If greater than .5 check for bad crossover cable, that's assuming the terminal connections are good.

 

[PWong]

when running drops down to around 11.
so I tested voltage at alternator when running and its up at 38 volts. surprised I haven't melted the batteries.

38V is the open circuit (no load) voltage of the alternator. It's like there is nothing connected to it. And there is NO charging current output. And hence non of the battery is getting charge. The load of the truck drains down the batteries.

You have a open circuit between the alternator output and the passenger side battery positive post.

 

[Ozymandias]

Blown fusible link?

 

[PWong]

There is NO charging current from alternator output to batteries.
The bridge between the alternator and the batteries is down.


Fusible links are after the batteries.

So check the charging cable and electrical connections at both ends.

 

[PWong]

When ALL the electrical connections between the alternator output and the batteries posts and grounds are perfect the voltage readings at alternator output, driver side battery positive post and passenger side battery positive post should be the SAME.
The charging path involve both the charging cable (first bridge) and the crossover cable (second bridge).